The present work performs a numerical investigation on the effect of Magnetic Resonance guided High Intensity Focused Ultrasound (MRgHIFU) on an obstacle in the blood vessel. A three-dimensional acoustics-thermal-fluid coupling model is employed to compute the acoustic and temperature field around the obstacle through blood vessel. The linear Westervelt equation and conjugate heat transfer equations are used for model construction. Finite Element Method is used to solve the governing equations. Results are shown graphically for the acoustic intensity, acoustic pressure field, temperature rise and velocity distribution at the obstructed region. This three-dimensional numerical study reveals that both the convective cooling and acoustic streaming can considerably change the temperature field at the obstacle through MRgHIFU therapy.